As terminal fittings for use in connection of an electric circuit, terminal fittings are known that include a metal base material made of a Cu alloy, and a Sn plating film that covers a surface of the metal base material. Terminal fittings include fitting-type terminals that are crimped to ends of electric wires, substrate terminals that are attached to circuit boards, and the like. These terminal fittings may be used alone, or may be used while being attached to connectors.
As a terminal material used for terminal fittings, a terminal material is often used that is obtained by stacking an Ni plating layer, a Cu plating layer, and a Sn plating layer sequentially on a surface of a metal base material made of a Cu alloy (Patent Document 1 JP2003-147579A). However, the terminal fitting disclosed in Patent Document 1 has a high friction coefficient because it has the relatively soft Sn plating layer at its surface, and needs a large terminal insertion force when being connected to a counterpart terminal fitting. Particularly when a terminal fitting is used while being attached to a connector, a multipolar connector that uses a plurality of terminal fittings is often employed, and thus a larger terminal insertion force is likely to be needed as the number of terminal fittings increases.
To reduce the terminal insertion force that is needed when a counterpart terminal fitting is fitted, a terminal fitting in which a Sn—Pd alloy-containing layer that is made of Sn and Pd is formed on a base material made of copper or a copper alloy has also been proposed (Patent Document 2 WO2013/168764A).